This research proposal is a combined neurophysiological, behavioral and immunocytochemical investigation of the structure of membrane receptors for tastants in primate taste buds. Thaumatin and miraculin are two proteins that in small quantities have very potent, long lasting effects exclusively in man and certain closely related primates. Thaumatin on a molar basis is 10 to the 4th power-10 to the 15th power times as sweet as sucrose. As little as 1 mg of miraculin (which in itself does not taste sweet) can make acids taste as if sugar has been added. Because all available data indicate that the rhesus monkey's response to these proteins is similar to that of man, this animal will be the experimental model. In neurophysiological experiments we shall study whole nerve and single fiber response to thaumatin, some derivatives of thaumatin, and thaumatin in combination with other compounds. In addition, we shall study the effects of miraculin on neural responses to tastants. In behavioral experiments we shall study the hedonic effects of thaumatin (and derivatives) and miraculin, both alone and in combination with other compounds. In immunocytochemical studies, our goals are a) to determine the location of binding sites for these proteins, and b) to relate the binding capacity of the proteins to their sweetness as revealed by physiological and behavioral studies. An important issue that may be resolved by these studies is whether or not there is more than one kind of sweet receptor in primate taste buds. The data may also be useful in understanding the molecular basis of dysgeusia and ageusia in man.